In a storage system comprising an information processing unit and a disk array unit connected thereto, it is known a function which stores a duplicate of data stored in a storage volume (hereinafter it is called a main volume) also in another storage volume (hereinafter it is called a sub-volume) to redundantly control data stored in the main volume (hereinafter it is called a duplication management function).
Also, as an operation technique of the duplication management function a technique is known which makes it possible to mutually shift between each condition of a condition in which when data is written to the main volume it is controlled to store a duplicate of the data in the sub-volume in real time (hereinafter it is called a pair condition) and a condition in which the pair condition is suspended and the data is not reflected to the sub-volume (hereinafter it is called a split condition).
Here, the shift from the pair condition to the split condition is performed, for example, when the user wants to use data in the main volume without affecting the information processing unit using the main volume. By shifting to the split condition, the sub-volume can be utilized for a use independent of the main volume. Here, as a process which applied to the sub-volume in the split condition, for example, there are a backup process, a process of accumulation or analysis of data, and the like.
After the process using the sub-volume is performed, the shift from the split condition to the pair condition is performed. Further, at this shift, a process to duplicate data which was not reflected to the sub-volume from the main volume to the sub-volume is performed prior to the shift to make the contents of the sub-volume consistent with the contents of the main volume.
As the prior art, refer to JP-A-2001-318833.